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The hunt for a substance that can improve memory took a promising turn Wednesday, as researchers said they had found a method that appears to reduce forgetting in rats.

According to a study published in the journal Nature, scientists from Mount Sinai School of Medicine in New York showed for the first time that a molecule that occurs naturally in the human brain during memory formation appeared to help rats enhance the strength and duration of some types of memories.

Researchers said that when the substance—known as IGF-II, a protein-like molecule important for cell growth and development as well as tissue repair—was blocked from the brain, the rats didn’t remember what they had learned.

The findings are notable in part because they showed improvement in an area of memory known as declarative memory—the ability to remember places, facts and things. Declarative memory is affected in Alzheimer’s disease and other forms of dementia, and researchers have long sought ways to improve or preserve it.

It is too early to say whether IGF-II will be useful in humans, but the substance may hold more promise than molecules that have been studied up to now, according to Elizabeth Phelps, a cognitive neuroscientist at New York University who studies human learning and memory. Dr. Phelps, who wasn’t involved in the study, called the Nature research “rigorous” and thoroughly conducted.

One advantage of IGF-II is that it can cross the blood-brain barrier, so it could potentially be administered through the bloodstream or as a vapor through the nose, rather than injected directly into the brain. And because it exists in the body already, it’s unlikely to be toxic.

However, researchers will watch for unwanted effects on other cells in the body, said Cristina Alberini, a neuroscience professor at Mount Sinai and the senior author of the paper.

Certain proteins and molecules are needed to build and strengthen connections between nerve cells in the brain to form new long-term memories, and IGF-II appears to be one of those molecules. But more research is needed, according to Dr. Alberini.

“The more we know, the more we’re going to uncover what are the steps that make memory strong,” she said. “Then we’ll get ideas for other [molecular] targets.”

In the study, the rats were placed in a two-compartment cage where they would receive a mild foot shock at one end. They quickly learned to avoid that area. Some rats were then given an injection of IGF-II, in a part of their brain called the hippocampus. Even weeks later, rats that had received the IGF-II exhibited greater avoidance of the location than rats that had a control injection of another growth factor or saline solution.

The effect was seen only in certain parts of the brain. IGF-II didn’t appear to improve memory in the amygdala, which deals more with memories of emotional reactions like fear.

The next step is to administer IGF-II to the entire body to see if it can produce the same memory-boosting effects as direct injection into brain regions, Dr. Alberini said.

On Dec. 23, Ronald Herrick gave a kidney to his twin brother. On Dec. 27, he died—56 years later.

Mr. Herrick, who was 79 when he died last month of heart ailments, was the world’s first kidney donor. Despite the experimental nature of the surgery, he recovered fully. His remaining organ expanded to do the work of two.

Back in 1954, a kidney transplant was only conceivable between identical twins like the Herricks. Today, thanks to immunosuppressant drugs, donors and recipients require little more than compatible blood types. With laparoscopic techniques, the largest incision required is just a couple of inches long, allowing a hospital stay of only two or three days.

But cultural norms haven’t kept up with medical advances. “People have called me crazy and looked at me like I have two heads,” says Diane Zocchia, who gave her cousin a kidney five years ago and works for the National Kidney Registry, a nonprofit group that facilitates living-kidney donation. “When they find out there is no financial gain,” says Ms. Zocchia, “they really think you’re nuts.”

More than 87,000 people are on the national waiting list for kidneys from deceased donors, a number that is growing steadily. In Los Angeles County, the average wait is now more than 10 years. Only living donors can make up the difference, and that requires changing attitudes.

Pop culture treats kidney donation as a sick joke. A famous “Saturday Night Live” parody commercial for “Bad Idea Jeans” equated giving someone a kidney to such “bad ideas” as having unprotected sex in Haiti or inviting a recovering free-base addict to live with you.

Most kidney comedy exploits the awkward tension between the need of the patient, a peripheral character, and the reluctance of the potential donor, a protagonist. The audience squirms in sympathy as the lead character struggles to avoid donating without actually saying no.

So Jack Donaghy (Alec Baldwin) of “30 Rock” organized a “Kidney Now” concert to help his father—and hide his own joy at being disqualified. On “Curb Your Enthusiasm,” Larry David spent a season scheming to avoid giving a kidney to his best friend. When he finally did donate, he nearly died. On TV, kidney donation is often dangerous and hence quite nuts.

The surgery does entail risk, but not as much as such plots suggest. About three in 10,000 living donors die of complications—a rate equivalent to an American woman’s risk of dying from pregnancy if she’s over 35. That’s not a risk that most people want to take, but neither is it unheard-of.

Surgeons, at least, have finally begun to accept the idea that perfectly sane people can find the benefit worth the risk. Already half the kidney transplants at the Ronald Reagan UCLA Medical Center come from living donors, and 40% of those are from the nonrelatives that centers used to turn down.

Even TV writers may be catching on. Last Sunday night something remarkable happened. Two prime-time shows included plots in which one character’s kidneys failed and, instead of the usual squirming, another character actively tried to donate. Admittedly, on “Family Guy” the would-be donor was a talking dog. But at the last minute a doctor, who treated donating as the logical choice, replaced him.

More significantly, on “Desperate Housewives,” where Susan (Teri Hatcher) is shown visibly ailing and facing years of dialysis, her mother’s refusal to donate seemed petulant and irrational. In contrast, against Susan’s protests her own daughter insisted on being tested. She told her mother: “They have these new surgical techniques—it’s no worse than a belly piercing—which I did not do.” An exaggeration, sure, but a welcome change from declaring kidney donation a Bad Idea.

—Ms. Postrel donated a kidney to a friend in 2006.Printed in The Wall Street Journal, page C12